This is a K01 award application for Judith Hahn, Ph.D., an epidemiologist at the University of California, San Francisco. Her long-term goal is to become a leader in developing mathematical models to guide health policy for drug users that are informed by empirical studies designed especially for this purpose. She has had extensive experience studying HIV and HCV in drug users and has authored 40 publications, including 7 as first author. However, her role as co-investigator on multiple studies for small amounts (10-15%) of her time limits her ability to develop her own research area, and while she is trained in biostatistics and epidemiology, she has had no previous formal training in mathematical modeling. K01 support will allow her to become skilled in (1) mathematical modeling of infectious diseases and (2) the conduct of multidisciplinary studies of disease transmission, especially partner studies, to inform such models. She will be mentored by Dr. Wayne Getz, Professor at DC Berkeley, an international leader in disease modeling. She will be co mentored by Dr. Kimberly Page-Shafer, Associate Professor, UCSF, who specializes in multidisciplinary HCV and HIV prevention studies. While HCV infects the majority of injecting drug users (IDU), promising vaccine candidates are in development and models are needed to evaluate their potential impact. In Aim 1, Dr. Hahn will construct a mathematical model to predict HCV trends in IDU in San Francisco, in the absence of new or intensified interventions. In Aim 2, she will then model the effects of several interventions, such as vaccination, increased drug treatment, behavior change, and HGV treatment strategies on the predicted prevalence and incidence of HCV in IDU. In Aim 3, she will conduct a multidisciplinary prospective study of HCV serodiscordant injecting partnerships to compare the infectivity of acute HCV infection and HIV/HCV coinfection to chronic HCV mono-infection and to estimate HCV infectivity for use in the mathematical models. She will leverage data and infrastructure from several large studies to achieve these specific aims. This research will form the basis for a modeling study of HCV interventions in different geographic and injecting settings, including settings of high HIV prevalence, to be proposed in an R01 application before the end of the K award. Public Health Relevance: This training and research will equip Dr. Hahn with the tools to conduct modeling studies based on solid epidemiologic data to guide the planning of effective interventions to reduce the HCV epidemic in IDU.